WO 2009103736 describes a vacuum infusion or vacuum assisted resin transfer moulding process (VARTM) process used for moulding fibre composite mouldings. In such a process uniformly distributed fibres are layered in a first mould part, the fibres being rovings, i.e. bundles of fibre bands, bands of rovings or mats, which are either felt mats made of individual fibres or woven mats made of fibre rovings. A second mould part, which is often made of a resilient vacuum bag, is subsequently placed on top of the fibre material. By generating a vacuum in the mould cavity between the inner side of the first mould part and the vacuum bag, the liquid resin can is drawn in and fill the mould cavity with the fibre material contained in the mould. So-called distribution layers or distribution tubes are used between the vacuum bag and the fibre material in order to obtain as sound and efficient distribution of resin as possible. In most cases the resin applied is polyester, vinyl ester or epoxy, and the fibre reinforcement is most often based on glass fibres or carbon fibres, but may also be plastic fibres, plant fibres or metal fibres.
The liquid resin is provided in a resin container, also called mixing bucket, filled with a resin/curing agent composition prepared in a mixing unit, adapted for mixing the resin monomer components and the curing agent in the respective amounts. As the curing reaction has already been started in the mixing unit, the exothermic polymerisation continuously raises the temperature in the resin container.
During the process of filling the mould, a vacuum, i.e. an under-pressure or negative pressure, is generated in the mould cavity, whereby liquid resin is drawn from the resin container or mixing bucket into the mould cavity via the inlet channels in order to fill said mould cavity. From the inlet channels the resin disperses in all directions in the mould cavity due to the negative pressure as a flow front moves towards the vacuum openings for generating vacuum inside the mould.
In the resin container such as the mixing buckets or the overflow container in such casting processes, e.g. blade casting methods for wind rotor blades, no solution exists for preventing the ignition of fire during the curing process which is caused by the exothermic reaction between the epoxy resin monomers and the curing agent. Conventionally, the mixing bucket is moved outdoors if signs of fire ignition or smoke development are observed in the mixing bucket to avoid any damages of the casting apparatus or the casting facilities and to protect the working environment of the staff around the blade mould.
U.S. Pat. No. 5,721,323 describes a prepreg containing a resin composition consisting of a polyepoxide, a curing agent, a catalyst for the reaction of the polyepoxide with the curing agent and a Lewis acid cure inhibitor for inhibiting the catalyst by means of forming a catalyst Lewis acid inhibitor complex. Cured and partially cured epoxy resins are used in coatings or laminates, wherein the inhibitor is used for inhibiting the curing reaction of polyepoxide by forming a stable complex between the curing agent and the Lewis acid in the prepreg and releasing the catalyst if a predetermined temperature level has been reached during the curing process. This inhibiting method is used for storing the polyepoxide resin composition in prepregs which are then used in moulding processes of composite parts. However, these prepregs are not used in casting process such as rein transfer moulding processes.